The present invention relates to a plasticized polyetherimide composition useful as a low temperature laminating adhesive More particularly, the present invention relates to the employment of a plasticized polyetherimide as a low temperature polyetherimide laminating adhesive in a high density interconnect circuit array which can be fabricated at temperatures of 260.degree. C. or below.
Prior to the present invention, high density interconnect structures utilized polyetherimide, such as Ultem polyetherimide, a product of GE Plastics Division, as a laminating adhesive for Kapton polyimide film, a product of E.I. duPont de Nemours Chemical Co, as shown in Eichelberger et al, U.S. Pat. No. 4,783,695. A typical procedure involved spray coating a polyetherimide solution onto a substrate having at least one integrated circuit (IC) chip followed by a bake step to effect the removal of the solvent. Kapton polyimide film was then laminated onto the substrate at 300.degree. C. as a first dielectric overlay. An argon ion laser was then used to ablate vias to the chip bond pads and allow fabrication of patterned metal interconnection from chip to chip and to external circuitry. If desired, additional dielectric layers could be laminated using a lower temperature thermosetting adhesive. Laser fabrication of vias followed along with the deposition of additional layers of patterned metal to complete the interconnection of the multi-chip device Although such procedures allow for the fabrication of various multi-chip integrated circuit packages, temperature sensitive electronic components, such as some gallium arsenide (GaAs) IC chips, frequently cannot be exposed to temperatures up to 300.degree. C. without impairing the electrical performance of the chips. A need exists therefore for an adhesive to provide an overlay layer on the surface of the substrate and chips which can be processed at temperatures of 260.degree. C. or below.
In addition to satisfying lower temperature requirements, the laminating adhesive also must adhere to substrates such as alumina, aluminum nitride, silicon, silicon nitride, components such as gallium arsenide, and various metals and polymer dielectrics, such as Kapton polyimide. There is also a need for solvent compatibility, optical absorbance at laser wavelength 351 nm for laser ablation, and flow characteristics at temperatures permitting additional polyimide dielectric layer laminations. If more Kapton polyimide dielectric layers are required, the melt viscosity of the initial laminating adhesive also must be sufficiently high to avoid movement of the base lamination layer during the application of the subsequently applied polyimide dielectric layers.